1. Field of the Invention
The present invention relates to an electric lamp having an outer envelope and an inner envelope, the inner envelope being supported within the outer envelope by a support member which is attached to a stem of the outer envelope, the attachment embodying an improved resilient and friction fit. A method of producing such a lamp is also disclosed.
2. Description of the Prior Art
Hermetically sealed lamps and tubes characteristically include a stem flare which extends into the sealed lamp or tube. Typically, the lead-in conductors are sealed within and extend through the stem flare to provide current to the device in a known manner. The lead-in conductors are attached to various of the components internal of the lamp or tube. It is known to support such components by means of one or more supports which are held in place vis-a vis the stem flare by a metallic band which is clamped to the stem flare. For example, U.S. Pat. No. 2,012,129 to A. W. Hull, which issued on Aug. 20, 1935 relates to a thermionic apparatus wherein the vibratory movement of electrodes is effectively damped by providing a substantially aperiodic support for the members which are subject to vibration. In particular, the support is in the form of a stranded cable or rod comprising parallel lines bound tightly together by a wire wrapped around the parallel wires. The upper end of the support is coupled to the members subject to vibration and the lower end is held in place by means of a sheet metal clamp which clamps the support and fits tightly over and pinches the press.
U.S. Pat. No. 2,059,902 to W. Persch, which issued on Nov. 3, 1936, relates to an electrode mounting for use with an electric discharge device. In this device an enclosing envelope is provided with a stem tube which extends into the device from a press having lead-in conductors sealed therein and extending therethrough into the enclosing envelope. The patent is of particular interest in that two supporting elements provide additional support for an electrode and a block of electron-emissive material, respectively. These two supporting elements are mounted vis-a-vis the stem tube by means of respective clamping rings which fit snugly upon the external surface of the stem tube such that each supporting element is sandwiched between a ring and the stem tube.
U.S. Pat. No. 2,069,814 to D. S. Bond, which issued on Feb. 9, 1937, relates to a gaseous discharge device employing an electron emitting cathode. Generally, the device includes an enclosing vessel having a hollow reentrant stem. It is of interest in that the electrode is supported by a plurality of rods which are welded to the outer surface of a split metallic collar which is clamped about the reentrant stem.
In U.S. Pat. No. 2,082,602 to H. C. Steiner et al., which issued on June 1, 1937, an electrical discharge device is provided which comprises an evacuated envelope which terminates in a press or stem. Within the envelope there are coaxially arranged a cathode structure, an electrostatic control member or grid and an anode. The grid is in the shape of a cylindrical cap which is supported a suitable distance from the cathode structure by diametrically opposed rods which are secured to an outer surface of a band of metal tightly embracing the stem.
U.S. Pat. No. 2,132,174 to R. R. Macklett, which issued on Oct. 4, 1989, relates to an X-ray tube which comprises a cathode which is mounted in the end of a split bushing which fits over the reentrant end portion of a neck of the envelope and is secured thereto by means of a metal sleeve such that the bushing is sandwiched between the reentrant end portion and sleeve.
U.S. Pat. No. 2,333,052 to C. G. Smith, which issued on Oct. 26, 1943, relates to an electrical discharge lamp comprising an evacuated transparent container which is mounted within an evacuated envelope and supported therein by spring arms which are carried by the outer peripheral surface of a clamping ring. The clamping ring is clamped around a reentrant stem.
U.S. Pat. No. 2,489,939 to E. K. Smith, which issued on Nov. 29, 1949, relates to an electron discharge tube which comprises an envelope having a control grid therein which is welded to the upper ends of hairpin supports. The lower ends of the supports are welded to a crimped collar. The grid is thereby supported within the envelope by the crimped collar on a circular mounting stem, the supports extending from the collar to the grid.
U.S. Pat. No. 3,229,140 to W. L. Vroom, which issued on Jan. 11, 1966, relates to an electron discharge tube comprising a conventional cylindrical cathode assembly which is supported in a glass envelope by two stiff bifurcated uprights. Each upright is welded at one end to the cathode assembly and at the other end to the outer surface of a metal collar. The metal collar is crimped tightly on a glass reentrant stem of the envelope to hold the cathode assembly in place.
In all of the foregoing structures, the clip-type mounting means engages a glass stem. It is necessary to sufficiently tighten the clip about the stem to hold the structure in place. However, tightening of the clip might crack the glass. A similar problem exists in providing mounts within electric lamps. In one embodiment which has been produced by the assignee of the present invention, a nickel plated stem clip has been used to support an arc tube mount. In such structure, the arc tube mount is welded to the stem clip, and the stem clip is then wrapped tightly around the body of the stem flare, the ends of the stem clip being welded together on the flat of the stem flare. This particular mounting embodiment has teen used in GTE Sylvania MP400/C/BU metal halide lamps discussed in greater detail herein. In such lamps, it has been difficult to reach a balance between the required degree of tightness of the stem clip about the stem flare, on the one hand, and the prevention of cracking of the glass stem on the other.
It is therefore an objective of the present invention to provide a means for mounting a support frame upon a glass stem in such a manner as to provide the required stability of the mount without damage to the glass stem flare.
It has also desirable to improve the insulative features of the arc tube frame support within the outer envelope of the lamp. In particular, it is desirable to improve the degree to which the arc tube support member is electrically isolated from the circuit of the lamp.